Thin disc, thick disc and halo in a simulated galaxy

C. B. Brook, G. S. Stinson, B. K. Gibson, D. Kawata, E. L. House, M. S. Miranda, Andrea Maccio, K. Pilkington, R. Roŝkar, J. Wadsley, T. R. Quinn

Research output: Chapter in Book/Report/Conference proceedingChapter

Abstract

Within a cosmological hydrodynamical simulation, we form a disc galaxy with subcomponents which can be assigned to a thin stellar disc, thick disc and a low-mass stellar halo via a chemical decomposition. The thin- and thick-disc populations so selected are distinct in their ages, kinematics and metallicities. Thin-disc stars are young (<6.6 Gyr), possess low velocity dispersion (ωU, V, W =41, 31, 25 km s-1), high [Fe/H] and low [O/Fe]. Conversely, the thick-disc stars are old (6.6 < age < 9.8 Gyr), lag the thin disc by ~21 km s-1, possess higher velocity dispersion (sU, V, W = 49, 44, 35 km s-1) and have relatively low [Fe/H] and high [O/Fe]. The halo component comprises less than 4 per cent of stars in the 'solar annulus' of the simulation, has low metallicity, a velocity ellipsoid defined by sU, V, W = 62, 46, 45 km s-1 and is formed primarily in situ during an early merger epoch. Gas-rich mergers during this epoch play a major role in fuelling the formation of the old-disc stars (the thick disc). We demonstrate that this is consistent with studies which show that cold accretion is the main source of a disc galaxy's baryons. Our simulation initially forms a relatively short (scalelength ~1.7 kpc at z = 1) and kinematically hot disc, primarily from gas accreted during the galaxy's merger epoch. Far from being a competing formation scenario, we show that migration is crucial for reconciling the short, hot, discs which form at high redshift in cold dark matter, with the properties of the thick disc at z = 0. The thick disc, as defined by its abundances, maintains its relatively short scalelength at z = 0 (2.31 kpc) compared with the total disc scalelength of 2.73 kpc. The inside-out nature of disc growth is imprinted in the evolution of abundances such that the metal-poor a-young population has a larger scalelength (4.07 kpc) than the more chemically evolved metal-rich a-young population (2.74 kpc).

Original languageEnglish (US)
Title of host publicationRelativity in Fundamental Astronomy
Subtitle of host publicationDynamics, Reference Frames, and Data Analysis
Pages690-700
Number of pages11
EditionS261
StatePublished - Apr 1 2009

Publication series

NameProceedings of the International Astronomical Union
NumberS261
Volume5
ISSN (Print)1743-9213
ISSN (Electronic)1743-9221

Fingerprint

halos
galaxies
stars
disk galaxies
time measurement
metallicity
refueling
simulation
annuli
ellipsoids
gases
metals
low speed
baryons
dark matter
time lag
kinematics
decomposition

Keywords

  • Disc-Galaxy
  • Evolution-galaxies
  • Evolution-Galaxy
  • Formation
  • Formation-galaxies
  • Galaxy

ASJC Scopus subject areas

  • Astronomy and Astrophysics

Cite this

Brook, C. B., Stinson, G. S., Gibson, B. K., Kawata, D., House, E. L., Miranda, M. S., ... Quinn, T. R. (2009). Thin disc, thick disc and halo in a simulated galaxy. In Relativity in Fundamental Astronomy: Dynamics, Reference Frames, and Data Analysis (S261 ed., pp. 690-700). (Proceedings of the International Astronomical Union; Vol. 5, No. S261).

Thin disc, thick disc and halo in a simulated galaxy. / Brook, C. B.; Stinson, G. S.; Gibson, B. K.; Kawata, D.; House, E. L.; Miranda, M. S.; Maccio, Andrea; Pilkington, K.; Roŝkar, R.; Wadsley, J.; Quinn, T. R.

Relativity in Fundamental Astronomy: Dynamics, Reference Frames, and Data Analysis. S261. ed. 2009. p. 690-700 (Proceedings of the International Astronomical Union; Vol. 5, No. S261).

Research output: Chapter in Book/Report/Conference proceedingChapter

Brook, CB, Stinson, GS, Gibson, BK, Kawata, D, House, EL, Miranda, MS, Maccio, A, Pilkington, K, Roŝkar, R, Wadsley, J & Quinn, TR 2009, Thin disc, thick disc and halo in a simulated galaxy. in Relativity in Fundamental Astronomy: Dynamics, Reference Frames, and Data Analysis. S261 edn, Proceedings of the International Astronomical Union, no. S261, vol. 5, pp. 690-700.
Brook CB, Stinson GS, Gibson BK, Kawata D, House EL, Miranda MS et al. Thin disc, thick disc and halo in a simulated galaxy. In Relativity in Fundamental Astronomy: Dynamics, Reference Frames, and Data Analysis. S261 ed. 2009. p. 690-700. (Proceedings of the International Astronomical Union; S261).
Brook, C. B. ; Stinson, G. S. ; Gibson, B. K. ; Kawata, D. ; House, E. L. ; Miranda, M. S. ; Maccio, Andrea ; Pilkington, K. ; Roŝkar, R. ; Wadsley, J. ; Quinn, T. R. / Thin disc, thick disc and halo in a simulated galaxy. Relativity in Fundamental Astronomy: Dynamics, Reference Frames, and Data Analysis. S261. ed. 2009. pp. 690-700 (Proceedings of the International Astronomical Union; S261).
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N2 - Within a cosmological hydrodynamical simulation, we form a disc galaxy with subcomponents which can be assigned to a thin stellar disc, thick disc and a low-mass stellar halo via a chemical decomposition. The thin- and thick-disc populations so selected are distinct in their ages, kinematics and metallicities. Thin-disc stars are young (<6.6 Gyr), possess low velocity dispersion (ωU, V, W =41, 31, 25 km s-1), high [Fe/H] and low [O/Fe]. Conversely, the thick-disc stars are old (6.6 < age < 9.8 Gyr), lag the thin disc by ~21 km s-1, possess higher velocity dispersion (sU, V, W = 49, 44, 35 km s-1) and have relatively low [Fe/H] and high [O/Fe]. The halo component comprises less than 4 per cent of stars in the 'solar annulus' of the simulation, has low metallicity, a velocity ellipsoid defined by sU, V, W = 62, 46, 45 km s-1 and is formed primarily in situ during an early merger epoch. Gas-rich mergers during this epoch play a major role in fuelling the formation of the old-disc stars (the thick disc). We demonstrate that this is consistent with studies which show that cold accretion is the main source of a disc galaxy's baryons. Our simulation initially forms a relatively short (scalelength ~1.7 kpc at z = 1) and kinematically hot disc, primarily from gas accreted during the galaxy's merger epoch. Far from being a competing formation scenario, we show that migration is crucial for reconciling the short, hot, discs which form at high redshift in cold dark matter, with the properties of the thick disc at z = 0. The thick disc, as defined by its abundances, maintains its relatively short scalelength at z = 0 (2.31 kpc) compared with the total disc scalelength of 2.73 kpc. The inside-out nature of disc growth is imprinted in the evolution of abundances such that the metal-poor a-young population has a larger scalelength (4.07 kpc) than the more chemically evolved metal-rich a-young population (2.74 kpc).

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